
Erasing free disk space
When you delete files by emptying the Trash, Mac OS X deletes the information used to access the files but doesn't actually delete the files. Although the disk space used by deleted files is marked as free space, deleted files remain intact until new date is written over them. Because of this, deleted files can be recovered.
You can use Disk Utility to erase the "free" space used by deleted files by having zeros written over the space once, seven times, or 35 times. If you have a lot of free space on your disk, overwriting the free space several times can take a long time.
Erasing free disk space does not erase the other files on your disk.
- In Disk Utility, select the disk or volume in the list with the free space you want to erase.
- Click Erase, then click the Erase Free Space button.
- Select an option, then click Erase.
After the process begins, you can interrupt it without harming your data.
You can also erase free space when you empty the Trash in the Finder. Choose Finder > Secure Empty Trash.